Substrate processing systems, such as physical vapor deposition (PVD) chambers, may use radio frequency (RF) signals to enhance substrate processing. For example, some systems may use multiple RF signals, such as a bias RF power, for example applied to an electrode disposed beneath a substrate, and a source RF power, for example applied to an electrode disposed in or near an upper region of the process chamber. The bias RF power may be used for example to control a DC bias formed on the substrate during processing and the source RF power may be used for example to form a plasma.
Typically, the frequencies of the bias RF power and the source RF power are determined by commercially available RF power equipment having specific available frequencies, and may be chosen according to the parameters of a specific processing application. For example, the substrate processing systems may be used for deposition and/or etching of materials in semiconductor device fabrication. The inventors have observed that in several instances, deposition and/or etching processes become unstable, for example when using bias RF power and source RF power under certain conditions.
Accordingly, the present invention provides methods and apparatus for stable substrate processing using multiple RF power supplies.